Micromachined gyroscopes are angular rate sensors that typically operate according to a physical phenomenon called the Coriolis Effect. The Coriolis Effect is, simply, the deflection of moving objects viewed from a rotating frame. For an object mounted to a substrate, the object tends to oscillate (e.g., vibrate, move, or drive) in a perpendicular plane when the substrate rotates. Hence, in order to make use of the Coriolis Effect, micromachined gyroscopes may be composed of an oscillating part comprising at least one mass, and a sensing part which is free to move in a perpendicular plane of the oscillating part. The sensing part is affected by the rotation of the gyroscope, as the oscillating part will be deflected. Under an external rotation, the oscillating mass deflects, and that deflection is sensed via the movement of the sensing part.
The sensitivity of such an oscillating gyroscope depends on its oscillation magnitude. In order to achieve a stable and large sensitivity, stable and large oscillation amplitude is desirable.
Typically, a large oscillation is achieved by using a one-degree-of-freedom (1-DOF) oscillator that is operated at its resonant frequency. Stability is then obtained with the help of stabilization circuitry (e.g., phase lock loops (PLLs), proportional integral (PI) controllers, etc.) to keep the gyroscope operating near this resonance frequency.
In some cases, the 1-DOF oscillator may be operated at non-resonance frequency, thereby reducing the need for stabilisation circuitry. However, a magnitude of the oscillation at non-resonance frequencies will be less than a magnitude of the oscillation at the resonance frequency. When the oscillator is oscillating at non-resonance frequencies, though, changes in the frequency, as well as the quality factor, will have a lesser effect on the oscillation magnitude, as compared to when the oscillator is oscillating at the resonance frequency.
Typical gyroscopes consume 10 to 20 times more power than a typical accelerometer in commercial applications. Some of this power consumption results from the comb-drive actuation used in typical gyroscopes to obtain large oscillation magnitudes. Comb-drive actuation involves electrostatic forces being generated between two comb-like structures. One comb is fixed to the substrate while the other comb is movable. The force developed by the comb-drive actuator is proportional to the change in capacitance between the two combs. However, this capacitance increases with driving voltage difference between both combs, with the coupling area reflected by the number of comb teeth, and the gap between these teeth. As a result, achieving large oscillation magnitudes with comb-drive actuation requires large polarization voltage differences, typically 12V in commercial devices. Such high polarization voltage differences are not conducive to a low-power gyroscope. Another source of this power consumption may be stabilization circuitry, such as PLLs and/or PI controllers, used to stabilize the oscillation increase power consumption of the gyroscope, which is similarly not conducive to a low-power gyroscope. Other sources of power consumption exist as well.
One option for reducing the power consumption of a gyroscope is to use a two-degree-of-freedom (2-DOF) oscillator that includes two masses and, accordingly, has two resonance frequencies. The 2-DOF gyroscope may be operated in between the two resonance frequencies. The amplitude response typically has minimal dependency on the varying quality factor and the resonance frequencies. However, the magnitude of this response is still very small and comparable to the non-resonance response of the 1-DOF oscillator discussed above.
Accordingly, a micromachined gyroscope with reduced power consumption may be desirable. It may be desirable for such a micromachined gyroscope to have a stable oscillation frequency range with a high mechanical amplification between the actuator and the driving part.